Scanning probe microscopes can be used for high resolution sample measurements. The lateral resolution of conventional optical microscopes is generally limited by diffraction effects, while in scanning probe microscope the resolution is limited by the dimensions of the scanning probe tip which is typically between about 5 nm and 100 nm. Some customary scanning probe microscopes include the atomic force microscope (AFM) and the near-field scanning optical microscope (NSOM). The AFM measures surface topographies by detecting a force exerted on a probe. In one configuration, a probe is secured to a cantilever, and deflections of the cantilever are estimated using laser beam illumination of the cantilever. The NSOM uses a probe having a small illumination aperture through which optical radiation is directed to a sample; and can be used to measure topographic and optical properties.
The AFM has been used to study frictional forces. A probe tip is dragged along a specimen surface and its lateral bending is monitored. This lateral bending is caused by frictional forces between the probe and the specimen. The smaller the bending experienced by the probe, the lower the frictional force. While such AFM-based measurements can provide useful insights into surface interactions, these measurements have significant limitations. For example, AFM-based measurements are associated only with frictional forces on the AFM probe, but provide no information on any effects on the sample, such as how energy is transferred to the sample by the probe. AFM-based measurements also provide limited information on any probe interactions with thin adsorbed fluid layers on specimen surfaces. Accordingly, methods and apparatus are needed that can provide enhanced specimen characterizations.